Mosquitoes in Palo Alto and Los Altos test positive for West Nile virus News

Mosquitoes have tested positive for West Nile virus in a small area of ​​Palo Alto and Los Altos, the Santa Clara County Vector Control District said Wednesday.

Areas including zip codes 94304, 94306 and 94022 will be treated starting at 10:00 p.m. Thursday to reduce the number of adult mosquitoes, weather permitting. The truck-mounted equipment will apply the treatment to the area in about four hours.

Notifications are sent directly to the public in treatment zip codes through AlertSCC and to those who subscribe to Nextdoor neighborhood networks. A general notice is issued on various social media platforms, including Facebook, Instagram and Twitter, and to those who subscribe to the district’s mosquito treatment notices.

West Nile virus arrived in California in 2003. More than 7,000 people across the state have contracted the disease; approximately 400 of these incidents were fatal. In 2021, 12 deaths related to West Nile virus were recorded; 2015 was a record year for deaths in the state with 55 deaths, the district said.

West Nile virus infection causes no symptoms in most people, but for some it can cause fever, headache, body aches, and, in severe cases, significant neurological damage or death. People with certain chronic conditions, such as diabetes, high blood pressure, cancer, and kidney disease, and the elderly are most at risk for serious complications.

The District’s conventional mosquito control program focuses on preventing mosquitoes from reaching the adult biting stage by targeting the immature stages of mosquitoes found mainly in standing water. When a mosquito with West Nile virus is detected, the district uses adult mosquito control to reduce the mosquito population in the area, which reduces the risk of West Nile virus-to-human infection.

It is normal for West Nile virus to increase in the summer and early fall because mosquitoes breed in warm weather. Although mosquitoes need water at every stage of life, they can still thrive in the drought conditions the state and county are currently experiencing.

Residents of the affected area do not need to relocate during treatment. When applied by a licensed vector control professional following area, label instructions, treatments pose minimal risk to people, pets, animals, and the environment.

Anyone who wants to take extra precautions can keep family members and pets inside with windows and doors closed during treatment hours. After sunrise, the insecticide breaks down quickly when exposed to sunlight.

The district applies insecticides at very low volumes so that people and pets do not inhale or touch anything with enough insecticide to be harmful. Anyone with a chemical sensitivity may want to see their doctor for further advice, the district said.

Treatment will be centered on Wilkie Way and West Charleston Road, bordering the following areas:

• North — St. Claire Drive, Chimalus Drive, Lambert Avenue, El Carmelo Avenue and Loma Verde Avenue.

• East — Middlefield Road, Christine Drive, Grove Avenue, Sutherland Drive, Park Boulevard, Waverly Street and Cowper Street.

• South — San Antonio Road, Showers Drive, Sherwood Avenue, McGregor Way, Miranda Avenue and Roble Ridge Road.

• West — Los Altos Square, Paso Robles Avenue, Santa Rita Avenue, Lavern Road and Alta Mesa Cemetery.

Treatment materials are approved by government environmental protection agencies and are widely used by vector control agencies throughout California by region.

The district said the public can help prevent the spread of West Nile virus by taking the following preventative measures:

By property:

• Check weekly for standing water.

• Empty or turn over anything that can hold water, such as flower pots, planters, pet bowls, buckets, and old tires.

• Clean items such as birdbaths and pet bowls once a week to remove mosquito eggs.

• Regularly clear debris from storm drains to allow water to flow.

• Properly screen rain barrels, cisterns, and irrigation channels to prevent mosquitoes from entering.

• Fix leaky faucets and broken sprinkler heads and prevent overwatering of lawns and plants.

• Make sure window and door screens are in good condition and fit tightly, with no holes or tears.

• Make sure the pool water level is adequate for proper circulation and filtration.

• Free mosquitofish can be requested online at for placement in maintenance pools/spas, ornamental ponds, water wells and other man-made bodies of water. For more information about our mosquitofish program, visit

Outdoor activities:

• Limit outdoor activity at dusk and dawn — these are the times when mosquitoes that transmit WNV are most active.

• If you spend time outdoors, wear long-sleeved shirts and long pants, preferably in light colors – mosquitoes are more attracted to dark colors.

• Always apply insect repellents containing DEET, IR3535, or Oil of Lemon Eucalyptus according to label directions.

Residents can contact the Santa Clara County Vector Control District if they are concerned about mosquitoes or know of a potential mosquito breeding source. For free help with mosquito control or other vectors, residents can call the district’s hotline at 408-918-4770 or submit a service request online.

Vector Control staff are available to answer any questions from the public at the dedicated West Nile Virus Hotline at 408-282-3114, Monday through Friday, 7:30 a.m. to 4:00 p.m. Questions can also be sent to the e-mail address [email protected]

More information on adult mosquito treatment products, including a safety data sheet, insecticide label and list of frequently asked questions, can be found at Additional information about mosquito control is available on the Centers for Disease Control and Prevention’s adulticide control webpage. For information on West Nile virus activity in California, visit

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